Impermeable, strong sheeting used for covers or protective barriers are necessary in a number of applications. Furthermore, continuous impermeable coverings for large areas or surfaces are particularly desirable in environmental, mining, and other projects relating to outdoor terrain.
Part of the difficulty involved in preparing an impermeable, strong covering involves the manufacture of a sheeting that can be augmented during the manufacturing process and further, easily fabricated to produce a continuous sheet of substantial size. The large size continuous sheets are desirable for use as barriers of excavation sites as well as top covers over excavation for containment. Significant outdoor uses include barriers used with ponds, land fills, waste disposal and hazardous waste management. In addition, continuous sheeting is used in mining operation to prevent leaching of potential dangerous chemicals used in refining. Other applications are in beachfront protection from oil spills, waterproof membranes and membrane stabilizers for road construction.
In these applications it is beneficial to have at least part of the continuous sheeting in contact with a textile layer. Typically, lengths of polymer sheets are laid over lengths of textiles. In the environmental applications the polymer sheets used as part of the barrier are often called geomembranes while the textile layer is called a geotextile.
A geomembrane can be plastic or rubber sheeting reinforced plastic or rubber sheeting of sufficient thickness or biaxially oriented plastic sheeting. Geomembranes, depending on the application, typically range in thickness from 5 mil-100 mil. The plastic sheeting alone in most instances is either too thin or sometimes too thick and rigid to provide effective protection against various mechanical stresses acting on the material. Problems can also occur from the accumulation of a liquid, such as ground water, vapor condensation or springs, or gas from organic degradation or air trapped in the soil underneath the plastic sheeting, causing it to burst. To prevent damage to the geomembranes, a geotextile is laid over the substrate or soil and the geomembrane is laid over the geotextile to protect and reinforce the geomembrane from damage due to rocks and sharp objects. The geotextile due to its porosity aids in the efficient drainage of liquids and gases, preventing costly membrane failure. The first reported use of such a combined arrangement was in 1971, although geomembranes and geotextiles reportedly were used separately starting in the 1940 and 1950's. These systems are now mandatory by governmental regulations for hazardous and nonhazardous waste landfills, waste piles, and other environmental applications. These systems perform better and have replaced the conventional clay/protective layers.
The geotextiles are made of nonwoven or woven material including fabrics, synthetic and natural fibers. Nonwoven textiles preferred for geotextile application are staple needle punched, continuous needle punched, spunbonded, melt blown, dry laid, wet laid, spunlaced, spunweb and composite structures. Installation is normally carried out on site. The ground is sufficiently conditioned before the installation of the geotextile. First, rolls of geotextile are laid over the area to be covered. Coverage is achieved by overlapping the rolls of geotextile with a 1-3 feet overlap, sewing the rolls together, or bonding with an adhesive at the site. The geomembrane or plastic sheeting is then rolled over the geotextile. The plastic sheeting can be sealed by field fabrication techniques, including extrusion fillet welding, extrosion flat welding, hot wedge fusion, hot air seaming and ultrasonic seaming. In these installations most of the work is carried out at the actual site where working conditions may be unreliable and further require a significant investment of time and labor.
The sealing techniques available on site can produce uneven seals resulting in a defective bond between layers of geomembrane. The seal may not be good enough to prevent leaks at the seam. Also, since in many cases the geotextile and geomembrane are simply laid on top of one another without any joinder between the two layers slippage can result particularly on a sloped area exposing one of the layers or ground beneath to moisture, hazardous waste or other type of leachate. Friction treatment on surfaces of the geomembrane or geotextile to prevent slippage have been proposed as shown in U.S. Pat. Nos. 5,056,960 and 5,137,393 issued to Marienfeld on Oct. 15, 1991 and Fuhr et al. on Aug. 11, 1992, respectively.
Hence, an improved system consisting of a fabric and polymer sheeting, offering the advantages of a simple fabrication technique, superior performance, ease of installation, versatility and economics is desirable.